Various circular members (circular members and annular members) such as bead members and cylindrical rubber members are used in the manufacture of a rubber product such as a tire. The inner circumferential length of such a circular member has a preset setting value designated by the design. However, due to a manufacturing error or the like, the actual inner circumferential length of the circular member may differ from the preset setting value. If this deviation is within a tolerance range, there is no problem. However, if outside of this tolerance range, the rubber product manufactured using the circular member may have quality problems. Thus, the inner circumferential length of the circular member needs to be measured and determined.
In the related art, various measuring devices for the inner circumferential length of an annular bead member have been proposed (for example, see Japan Unexamined Patent Publication Nos. 2012-150013 and 06-1128). In the device described in Japan Unexamined Patent Publication No. 2012-150013, a cylindrical measurement support including two semicylindrical sections is disposed on the inner side of a bead member. In measuring the inner circumferential length of the bead member, the sections are moved away from each other and the outer circumferential surfaces of the sections are put in close contact with the inner circumferential surface of the bead member. The separation distance between the sections at this time and the circumferential length around the outer circumferential surfaces of the sections are used to measure the inner circumferential length of the bead member. However, because the outer circumferential surfaces of the sections are put in close contact with the inner circumferential surface of the bead member, force pushing to expand the diameter of the bead member is applied. This may cause deformation. Thus, this is not advantageous in improving the accuracy in measuring the inner circumferential length.
In the device described in Japan Unexamined Patent Publication No. 06-1128, a roller is directly brought into contact and pushed against an inner circumferential surface of a bead member. The roller is rolled along the inner circumferential surface of the bead member for one rotation in the circumferential direction. The number of times the roller rotated is used to measure the inner circumferential length of the bead member. However, because the roller directly comes into contact and pushes against the inner circumferential surface of the bead member, deformation may occur. Thus, this is not advantageous in improving the accuracy in measuring the inner circumferential length.